Needle-free injection devices provide an alternative to standard fluid delivery devices, which typically use a needle adapted to penetrate the outer surface of an injection site. Typically, needle-free injection devices are designed to eject the fluid from a fluid chamber with sufficient pressure to allow the fluid to penetrate the target to the desired degree. For example, common applications for needle-free injection devices include delivering intradermal, subcutaneous and intramuscular injections into or through a recipient's skin. For each of these applications, the fluid must be ejected from the system with sufficient pressure to allow the fluid to penetrate the tough exterior dermal layers of the recipient's skin.
Needle-free injection devices often employ pressurized gas to generate the force required to deliver injections. Various seals must be employed in such a device, so that as pressurized gas is applied, the resulting energy is captured and used effectively to deliver the injection. Inadequate sealing can result in waste of pressurized gas and/or an undesirable loss of control over the pressure at which the injection is delivered. In addition to sealing, various other design considerations are involved in providing injections with desired pressure characteristics.
Gas-powered and other needle-free injection devices may in some cases be pre-filled and/or configured to be used only once before disposal. With these devices, it will normally be desirable to reduce or eliminate the ability of an end user to disassemble or otherwise tamper with the device, or to use it other than as intended. Also, it will often be desirable to minimize manufacturing costs, accommodate different desired dosages with minimal modifications to the device and/or fabrication processes, and reduce contamination and other safety risks during and after use of the device.